Functional evidence for the identification of an Arabidopsis clathrin light chain polypeptide.

Clathrin light chains (CLCs) are regulatory subunits of clathrin triskelia. Based on homology searches in Arabidopsis thaliana data bases we have identified three putative CLC clones, and have focused on the one with the highest homology to mammalian CLC sequences. Analysis of its sequence has revealed coiled-coil structures within a region that corresponds to the clathrin heavy chain-binding site. In addition there is a stretch of acidic amino acids, which is required for the regulatory function of CLC in clathrin assembly. This putative plant CLC ortholog, expressed in bacteria as a glutathione-S-transferase- and myc-tagged fusion protein, was shown to bind to CLC-free recombinantly expressed mammalian clathrin hubs. In contrast, purified native mammalian triskelia with endogeneous CLC did not bind the recombinant putative plant CLC. Based on the conserved sequences between the three Arabidopsis candidates it appears that plants, unlike mammals, may have more than two CLCs.